Field of the Invention
The invention relates to an electromagnetic multiple actuator, in particular an actuator for two gas exchange valves of an internal-combustion engine.
Actuators for gas exchange valves of internal-combustion engines are known. Unlike camshaft-actuated valves, electromagnetically driven valves are made to open and close in dependence on the rotational position of the crankshaft. The actuator must thereby be able to apply high forces, in particular when opening a discharge valve, and the respective limit position of the gas exchange valve has to be reliably reached during opening and closing.
An electromagnetic actuator is disclosed, for example, in the commonly assigned U.S. Pat. No. 6,016,778 (see German patent DE 197 35 375 C2). That actuator has an armature which is held in a center position between two electromagnets by two springs. When current is applied to one of the electromagnets, the armature is drawn into the respective limit position associated with the electromagnet and it can be held in that position. To transfer the actuator and therefore the gas exchange valve driven by it from one limit position into the other, the application of current to the holding coil is ended, and current is applied to the other coil. As a result, the armature is moved into the other limit position under the force of the springs and of the electromagnet which has been switched on.
To control the movement of the actuator, for example to control the valve movement in an internal-combustion engine, the lifting movement of the actuator has to be continuously measured. In an internal-combustion engine, the valve lift of a gas exchange valve is usually 8 mm.
This lift has to be measured to an accuracy of approximately 1/100 mm to allow effective valve control.
To achieve this, it is known to measure the inductance of the winding of an electromagnet (see U.S. Pat. No. 5,238,098 and European patent application EP 0 500 389) or to use an eddy-current sensor or an optical position sensor (see U.S. Pat. No. 5,072,700 and European patent application EP 0 493 634) in order to detect the position of the armature.
The electromagnetic drive of the actuator has to apply considerable forces, with the result that, firstly, the surface area of the armature and of the electromagnets should be selected to be as large as possible, and secondly there is a considerable thermal load on the electromagnets. However, the space available for an actuator which drives, for example, a gas exchange valve of an internal-combustion engine is limited.
One possibility of solving the thermal problems with an actuator of this type would be connection to a cooling circuit, for example to the cooling circuit of an internal-combustion engine. However, this would require an unacceptably high level of outlay.
Furthermore, the abovementioned actuators are relatively difficult to assemble, since they are constructed from a large number of individual parts.
It is accordingly an object of the invention to provide an electromagnetic actuator, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which is of compact design, is able to apply high forces, and does not need to be connected to a cooling circuit.
With the foregoing and other objects in view there is provided, in accordance with the invention, an electromagnetic multiple actuator, in particular for the gas exchange valves of an internal combustion engine. The actuator comprises:
a housing and at least two armature shafts extending through the housing, with each of the armature shafts having an armature attached thereto;
two electromagnets for each armature, each electromagnet having a coil core and a winding with the respective armature disposed between;
first and second springs respectively acting on each armature in opposite directions and forcing the armature into a position of repose between the electromagnets, and wherein each first spring is clamped between a part of the housing and an armature spring cup attached to the armature shaft.
In the novel concept according to the invention at least two individual actuators are combined to form a multiple actuator. A multiple actuator of this type has a housing, through which at least two armature shafts run, to each of which an armature is secured, which lies between two electromagnets and is held in an at-rest position, i.e., a position of repose, by two springs.
This construction enables the multiple actuator to bear over a large area against a cooled surface, for example the cylinder head of an internal-combustion engine, on the underside, i.e. the side which, for example, faces the gas exchange valves in an internal-combustion engine. In this configuration, the available surface area of this cooled part is optimally covered by the multiple actuator, since the gap which normally remains between individual actuators is no longer present. The combination of a plurality of individual actuators in one housing enables the surface areas of the armatures and their electromagnets to be maximized. Finally, the large-area side wall of the multiple actuator provides good thermal coupling of the top side of the actuator to the underside which bears against the cooled part.
In accordance with an added feature of the invention, the housing has a top side and a housing underside that is in contact with a cooled part. The housing is formed, on at least one side wall thereof, to assure good heat dissipation from the top side to the cooled housing underside.
In accordance with an additional feature of the invention, each armature shaft is guided in bushes inserted into the housing top side and the housing underside.
In accordance with another feature of the invention, washers are disposed to support the first springs on the housing, and the washers are adjustable in an axial direction for setting a spring force of the springs.
In accordance with a further feature of the invention, the housing is formed in two parts connected by bolts running through at least one side wall of the housing. The housing parts, in a further preferred embodiment of the invention, are produced by breaking apart a single-part housing, ensuring that the housing parts fit together. The construction according to the invention further reduces the number of parts in the actuator, which considerably simplifies assembly. The housing is thus initially produced as a single part and is then broken at desired breaking points, so that an optimum fit is achieved after the housing parts have been fitted together and are held together by bolts which run through at least one side wall.
In accordance with again an added feature of the invention, more than two armature shafts with respective armatures and associated electromagnets are provided, and the housing has a divider between two armatures and their electromagnets. The divider preferably has guide elements guiding at least one armature along an axis of the armature shaft.
In accordance with again a further feature of the invention, the coil core is a common coil core for a plurality of electromagnets.
With the above and other objects in view there is provided, in accordance with the invention, a combination of a cylinder head of an internal combustion engine with the multiple actuator according to the above-outlined invention for actuating gas exchange valves of the internal combustion engine. In that case, the second springs are each clamped between a valve spring cup attached to a valve shaft of the driven gas exchange valve, and the cylinder head wherein the gas exchange valves are guided.
The springs preferably lie outside the housing. This makes the coil cores easier to secure.
The housing is also responsible for the longitudinal guidance of the armatures along the axis of the armature shaft, so that there is no need for a separate rotational securing means, as is required in the prior art, since, on account of the longitudinal guidance, the armature can no longer follow the rotation caused by the springs.
The measurement of the position of the armatures of each actuator part is preferably carried out by contactless measurement by means of magnetic field-sensitive measurement sensors which are attached to the housing of the multiple actuator, and associated permanent magnets, which are each arranged in a fixed position with respect to the armature. Each permanent magnet generates a stray magnetic field. The associated magnetic field-sensitive measuring sensor, the signal of which is preferably dependent only on the direction of the magnetic field, records the position of the permanent magnet and therefore the position of the armature. If the multiple actuator drives gas exchange valves of an internal-combustion engine, the position of the armature is associated with that of the corresponding gas exchange valve.
The principle according to the invention can be applied to entire actuator arrays, for example all the actuators belonging to the inlet side or the outlet side of an internal-combustion engine can be combined in one actuator array. In order then to ensure the guidance of the armatures, it is possible to provide perpendicular dividing walls in the housing.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an electromagnetic multiple actuator, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.